docs: def do_cancel(self, taskid: int) -> None:
          """Cancel an indicated task"""
          task = task_by_id(taskid, self._loop)
          if task:
              fut = asyncio.run_coroutine_threadsafe(
                  cancel_task(task), loop=self._loop)
              fut.result(timeout=3)
              self._sout.write('Cancel task %d\n' % taskid)
          else:
              self._sout.write('No task %d\n' % taskid)